Growth on Bettas underside?

This is Agony- I've had him two years now.
The last six months he has had a little growth on his underside, between his fins. It is white.
I'm not sure what it is, but it didn't seem to bother him and he never acted differently so I didn't worry too much about it, and just stuck to twice weekly water changes.

Well the growth had gotten larger recently, and the last two days he has been resting on the bottom or bobbing at the surface, not all the time and not favoring the surface or floor, but definitely a noticeable change.
Appetite is still good, he is active and alert, swims well etc.
He is in a 5 gallon portrait aquarium, its been running for 2 and a half years, filter is strong and I wash the media in tank water once weekly during a water change.
So what could this be? Is it a tumor?
I did my best to get some pictures but he is very quick.

It could be an ulcer, or an abscess. It’s rare for cancerous lumps to form, though I’ve had it happen once. But since yours is white, it’s likely not. This can be caused by them rubbing up onto something sharp, or some kind of other injury. Maintain clean water and it SHOULD heal on its own. Look for any red, if there’s some red, it’s an ulcer. And if not it could be an abscess. Check your water parameters

That looks similar to the one my betta had last year. your description of the fish's behavior being completely normal is exactly what mine was like until it suddenly became less active. (mine used the stem plants to rest on)
I sadly had to put the fish down after it grew very large even having a pocket of liquid forming on the side, which made the fish uncomfortable with it even rubbing it against the glass. I assumed that mine was a tumor as these fish are sadly prone to forming these problems however I'm still 100% sure what it was. Hopefully, it doesn't affect the fish as badly as mine had it. What a beautiful fish you have as well

I had a white spot growth similar to @MattW3344 did on a Betta, but might was on the fleshy part of the tail. The growth on my betta would grow, then shrink then grow again. I examined the fish mid way under a microscope but could find anything. Eventually after a year of this the fish started not doing well and I euthanized her.

There are a lot of cases of growths on Bettas it seems. I would say more than on other fish by this forum, though that could simply be more people keep bettas.

MattW3344 said:

That looks similar to the one my betta had last year. your description of the fish's behavior being completely normal is exactly what mine was like until it suddenly became less active. (mine used the stem plants to rest on)
I sadly had to put the fish down after it grew very large even having a pocket of liquid forming on the side, which made the fish uncomfortable with it even rubbing it against the glass. I assumed that mine was a tumor as these fish are sadly prone to forming these problems however I'm still 100% sure what it was. Hopefully, it doesn't affect the fish as badly as mine had it. What a beautiful fish you have as well

Click to expand...

Uberhoust said:

I had a white spot growth similar to @MattW3344 did on a Betta, but might was on the fleshy part of the tail. The growth on my betta would grow, then shrink then grow again. I examined the fish mid way under a microscope but could find anything. Eventually after a year of this the fish started not doing well and I euthanized her.

There are a lot of cases of growths on Bettas it seems. I would say more than on other fish by this forum, though that could simply be more people keep bettas.

Click to expand...

Crunchycrouton said:

It could be an ulcer, or an abscess. It’s rare for cancerous lumps to form, though I’ve had it happen once. But since yours is white, it’s likely not. This can be caused by them rubbing up onto something sharp, or some kind of other injury. Maintain clean water and it SHOULD heal on its own. Look for any red, if there’s some red, it’s an ulcer. And if not it could be an abscess. Check your water parameters

Click to expand...

Thanks everyone, sorry it took me so long to respond.
Agony is getting worse, I noticed a smaller but identical white growth on his tail fin a few days ago, and now the white on his face is starting to grow as well (until now this white has presented as coloration, he was almost all white when I first bought him but eventually turned blue, I'll include pictures below).

I am thinking it is some kind of cancerous growths, very unfortunate. I've been doing water changes every other day, ammonia, nitrites, and nitrates all read as 0.
He is still eating, just not as much or as eagerly, and he is losing weight and is noticeably thinner.
Some of his scales are starting to look disheveled, some are peeling up from his skin, not quite pineconeing but just random scales.

All growths are looking larger every few days.
I'm sad, but I've had him a long time and until now he has had no issues. I got him November 2021.
Here are pictures.
Any advice is really appreciated but I'm not thinking this is something I can fix. If he gets worse, how do I euthize him?
Here are pictures of him when I first got him- he's probably IMO the most beautiful fish I've ever had.